Sustainable nutrient practices in Werribee and Bacchus Marsh
Frankie Ruffo (left), Bacchus Marsh Tripod Farmers and Julio Vargas (right)
This project worked with a group of vegetable growers in the Werribee Catchment, measuring various nutrient concentrations in the soil to determine if these nutrients were being fully utilised or wasted.
The overall aim of the project was to improve the nutrient use efficiency of the vegetable industry within the Werribee catchment as well as reduce nutrients loads to Port Phillip Bay.
Information gathered from this project indicates that 30% of the industry is wasting large amounts of fertiliser. Approximately 10% of Vegetable growers from the Werribee and Bacchus Marsh irrigation districts were involved in the project. From this sample size the project determined that:
- 30% of industry has good nutrient practices,
- 40% of industry has average nutrient practices due to a certain amount of over application of fertilisers,
- 30% of industry has poor nutrient practices due to very high over application of fertilisers.
Results from weekly monitoring of nutrients in the soil alerted some farmers to change their nutrient program. Savings of up to $400 to $700 for broccoli and cauliflower per hectare for nitrogen can be made just by managing nutrient in an efficient way (see Table 1).
Crops studied in the project included broccoli, cauliflower, artichoke, fennel, lettuce, Asian vegetables crops and salad crops. Nutrients were extracted at 30 and 50 cm depths, i.e. at the rootzone and below the rootzone for most of the crops. These were nitrogen, phosphorous, potassium, calcium plus pH and EC
Analysis of Nitrate
Analysis of the soil moisture extractions indicated that at harvest time NO3 was depleted at 30 cm, yet at the 50cm depth a reasonable amount of NO3 was left in the soil. This indicated that it is most probable that NO3 will leach though the soil as the wetting front goes further down the profile.
Fertilisers and salinity
Virtually all fertiliser materials are salts. An increase in salt concentration increases the osmotic potential of the soil solution. The higher the osmotic potential of a solution, the more difficult it is for seeds or plants to extract soil water they need for normal growth (Salt Index of Fertilisers, 1986).
Initially the salinity of the soil solutions were found to be high at planting and development stages. Although there is an issue with salinity in the Werribee area, EC values at harvest time were found to be lower than expected. This is probably because nutrients were leached through the soil profile with some nutrients taken up by plants. A balance between irrigation to remove salts and fertiliser timing can be achieved through good fertigation practices.
Soil pH affects the availability of most nutrients to be taken up by plants. The project found that for all the soils in the Werribee and Bacchus Marsh irrigation district, pH values were within the right range for growing crops.
|Crop||kg of nitrogen leached below 50 cm||cost of fertiliser wasted/ saved (estimated @$1.50 per kg)|
The National Executive of the Australian Fertiliser Services Association (AFSA) a supporter of the project said that one of the critical issues with the overuse of fertilisers is the inaccurate application of products due to poor quality, untested equipment. Often, growers have little understanding of the accuracy of their equipment. The AFSA AccuSpread program has the capability of certifying and accrediting the spreading capability of spreading equipment.
Practices to improve nutrient applications (vegetablesWA – Good Practice Guide)
Suction cups (lysimeters) installed on Lettuce crop
Know your crop's nutritional needs and select the most appropriate fertiliser.
Recognising deficiency in a crop can help in the assessment of nutrient requirements.
Reduce leaching of nitrogen by managing the rate and timing of its application, and through the use of appropriate irrigation practices.
Return plant material to the soil
For example, incorporate crop residues into the soil.
Soil sampling. Measure the nitrogen, phosphorus, potassium, sulphur, calcium and magnesium amounts in the soil. Determine the physical, chemical and biological properties of your soil. Consider possible nutrient deficiencies or toxicities. Plan fertiliser programs, and monitor long-term fertility trends.
Plant tissue/sap analysis. Use tissue/sap analysis to help you: diagnose or predict nutrient deficiencies or toxicities, and monitor the adequacy of your fertiliser program, making adjustments as necessary.
Irrigation water testing. Have your water supply analysed for both quality and nutrients (groundwater may contain many of the nutrients supplied by fertilisers). Adjust your fertiliser program accordingly.
Timing of nutrient application. Consider growth stage of the crop, type of fertiliser applied and how often, and schedule irrigation with rainfall.
Quantity of fertiliser. Understanding the nutrient composition of fertilisers will help you decide what to apply and when.
Manure as a nutrient source. In addition to their nutrient values, organic manures help improve the physical properties of the soil, thereby improving its water and nutrient-holding capacity.
Compost as a nutrient source. For growers to maximise the benefits of compost, they need to adjust their fertiliser programs to account for these extra nutrients.
Selection of fertiliser. The choice of fertiliser should not depend on price alone. The following factors should be taken into consideration - Response to fertiliser and nutrients currently in the soil. Is the fertiliser available locally? What package size is easiest to manage? Is the fertiliser safe to apply?
On-farm trials. Fine-tune your fertiliser application methods, rates and timing by conducting annual 'strip trials' on your property.
Contact Julio Vargas – (03) 5366 0048 or firstname.lastname@example.org